This invention relates to means for positioning and retaining a bobbin case in operating engagement with the loop taker of a sewing machine.
Bobbin case retaining and positioning means having no operator actuatable parts are known in the art. See for example, U.S. Pat. No. 3,373,707, Mar. 19, 1968, Ketterer, the teachings of which are incorporated herein by reference. Such construction permits insertion or removal of the bobbin case by the operator without the need to manipulate a locking lever or other similar device. This very feature, however, permits the bobbin case to move out of position for correct operation under certain operating conditions. That is because the bobbin case can be inserted into and removed from operating position within the controlled embrace of the bobbin case retaining bracket, without manipulation of a locking means, the bobbin case may be urged out of operating position by vibrational and other forces that normally occur within an operating sewing machine. This frequently affects the appearance of the stitches or results in bobbin thread breakage. Other constructions, on the other hand, utilize a locking device which may be manipulated by the operator for retaining the bobbin case in operating position. Such locking devices usually take the form of a sliding or pivoting member that may be positioned so that removal of the bobbin case from its operating position is blocked. See, for example, U.S. Pat. No. 4,292,906, Oct. 6, 1981, the rights of which are owned by the assignee of the present invention and the teachings of which are incorporated herein by reference. Such constructions have the disadvantages inherent in assemblies of multiple parts such as difficulty in precisely positioning the parts due to tolerance build up and increased manufacturing and maintenance costs due to the more complex construction.
The present invention overcomes these disadvantages through the use of a novel but simple device.